1. Field of the Invention
The present invention relates to the field of computer displays, and in particular to a method and apparatus for hardware acceleration of display data clipping.
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2. Background Art
In a computer system, a computer may receive data to present to the user using a display device (e.g., a monitor) from multiple sources. For example, a video window with streaming video may be supplied by one source, and a text window may be supplied by another source. The source may be located at the computer attached to the display device, or it may be located at another computer. Typically, in a thin client architecture, display information source are not located at the terminal attached to the display device.
In some instances, the regions of display for two sources may overlap. Display data for the covered portions of the video window must be discarded, or clipped, rather than displayed. In prior art solutions, software systems are used to clip unneeded display data. However, software clipping is slow and inefficient. This problem can be better understood with a discussion of display systems in a multi-tier application architecture.
Mufti-Tier Application Architecture
In the mufti-tier application architecture, a client communicates requests to a server for data, software and services, for example, and the server responds to the requests. The server's response may entail communication with a database management system for the storage and retrieval of data.
The mufti-tier architecture includes at least a database tier that includes a database server, an application tier that includes an application server and application logic (i.e., software application programs, functions, etc.), and a client tier. The data base server responds to application requests received from the client. The application server forwards data requests to the database server.
FIG. 1 provides an overview of a mufti-tier architecture. Client tier 100 typically consists of a computer system that provides a graphic user interface (GUI) generated by a client 110, such as a browser or other user interface application. Conventional browsers include Internet Explorer and Netscape Navigator, among others. Client 110 generates a display from, for example, a specification of GUI elements (e.g., a file containing input, form, and text elements defined using the Hypertext Markup Language (HTML)) and/or from an applet (i.e., a program such as a program written using the Java™ programming language, or other platform independent programming language, that runs when it is loaded by the browser).
Further application functionality is provided by application logic managed by application server 120 in application tier 130. The apportionment of application functionality between client tier 100 and application tier 130 is dependent upon whether a “thin client” or “thick client” topology is desired. In a thin client topology, the client tier (i.e., the end user's computer) is used primarily to display output and obtain input, while the computing takes place in other tiers (i.e., away from the thin client). A thick client topology, on the other hand, uses a more conventional general purpose computer having processing, memory, and data storage abilities. Database tier 140 contains the data that is accessed by the application logic in application tier 130. Database server 150 manages the data, its structure and the operations that can be performed on the data and/or its structure.
Application server 120 can include applications such as a corporation's scheduling, accounting, personnel and payroll applications, for example. Application server 120 manages requests for the applications that are stored therein. Application server 120 can also manage the storage and dissemination of production versions of application logic. Database server 150 manages the database(s) that manage data for applications. Database server 150 responds to requests to access the scheduling, accounting, personnel and payroll applications' data, for example.
Connection 160 is used to transmit data between client tier 100 and application tier 130, and may also be used to transfer the application logic to client tier 100. The client tier can communicate with the application tier via, for example, a Remote Method Invocator (RMI) application programming interface (API) available from Sun Microsystems™. The RMI API provides the ability to invoke methods, or software modules, that reside on another computer system. Parameters are packaged and unpackaged for transmittal to and from the client tier. Connection 170 between application server 120 and database server 150 represents the transmission of requests for data and the responses to such requests from applications that reside in application server 120.
Elements of the client tier, application tier and database tier (e.g., client 110, application server 120 and database server 150) may execute within a single computer. However, in a typical system, elements of the client tier, application tier and database tier may execute within separate computers interconnected over a network such as a LAN (local area network) or WAN (wide area network).
Display Systems
Display systems in the multi-tier application architecture are used to arrange display information for presentation to a user on a display device (e.g., a monitor) in the client tier 100. Typically, a display system comprises a display memory and a display controller. The display memory is typically dynamic random access memory (DRAM) and contains pixel color information for each pixel of the display device. The display controller updates the data in the display memory and retrieves data from the display memory to send to the display device.
Frequently, the desired display areas of two display data sources overlap. For example, video data may be transmitted to a client terminal from two different data sources in a thin client architecture and the windows displaying the video data may be overlapping. Since both windows cannot write to the display memory for the overlapping pixels, the video information for the overlapping area of the rear window must be clipped. Furthermore, any portions of the video window which is off the screen must be clipped.
Clipping is typically performed by software. The software saves the desired display data and discards the rest. Then, only the desired display data is passed on to the display system for eventual display. In some systems, the clipping software runs on a different computer from the computer (of the client tier 100) directly attached to the display system.
Clipping in Thin Client Architectures
In some prior art thin client architecture systems, display data is clipped using software before it is transmitted to the client terminal. However, this approach is difficult and inefficient to coordinate when display data is transmitted from separate source locations. The approach encounters additional problems when display data is being multicast to many client terminals. The clipping may be different for each client terminal receiving the display data, so it is inefficient for the data source to perform clipping before transmitting the data to each client terminal.